Self-assembly of naturally occurring stigmasterol in liquids yielding a fibrillar network and gel

Abstract

Stigmasterol, a naturally occurring 6-6-6-5 monohydroxy phytosterol, was extracted from the leaves of Indian medicinal plant Roscoea purpurea, commonly known as Kakoli. In continuation of our studies on the self-assembly properties of naturally occurring terpenoids, herein, we report the first self-assembly properties of this phytosterol in different organic liquids. The molecule self-assembled in organic liquids yielding supramolecular gels in most of the liquids studied via the formation of fibers and belt-like architechtures of nano-to micrometer diameter. Characterization of the self-assemblies carried out by using scanning electron microscopy, transmission electron microscopy, atomic force microscopy, optical microscopy, FTIR and X-ray diffraction studies indicated fibrillar network and belt-like structures. A model for the self-assembly of stigmasterol has been proposed based on molecular modeling studies, X-ray diffraction data and FTIR studies. Rheology studies indicated that the gels were of high mechanical strength. Fluorophores such as rhodamine B, carboxy fluorescein including the anticancer drug doxorubicin could be loaded in the gels. Moreover, release of the loaded fluorophores including the drug has also been demonstrated from the gel phase into aqueous medium.